The document summarizes evidence from the fossil record for the evolution of whales from terrestrial mammals. It describes how whales have been found to possess vestigial hind limbs and describes a series of transitional whale fossils from Pakicetus, Ambulocetus, and Rodhocetus that show whales evolving from four-legged land-dwelling creatures to fully aquatic mammals over tens of millions of years. It also notes how the number of whale species increased dramatically over the Eocene period, representing one of the clearest examples of macroevolution seen in the fossil record.